The invention relates to belt-type conveyor systems, and more particularly to the conveyor systems which carry bulk materials, such as for carrying crushed stone, gravel, coal and the like. Commonly, the upper runs of the conveyor belts are supported on conveyor belt idlers, which from a particularly troughing angle with the upper run of the belt. Such conveyor systems have a loading or impact zone, where the material to be carried by the belt is loaded onto the belt surface. The force of the loading of the material, at the loading zone, applies a particularly high stress to the belt and to belt-supporting idlers.
Commonly, special idler rollers are used in the loading zone, known as impact rollers, which are specially constructed to absorb the loading impact forces. An impact idler assembly is a heavy-duty version of the normal conveyor belt idler, in which the rollers are more resistant to impact loading. The rollers, themselves, are usually three in number, that is, two side rollers and a bottom roller, mounted for rotation on a common support frame, and the rollers may be formed with a cushioning surface, such as in the form of a stack of discs, to resist impact. A good example of an impact idler consists of the stacked rubber disc impact idler, types HG and HS, of Continental Conveyor & Equipment Company, Inc., Windfield, Ala. 35594. Thus the conventional idler roller assembly consists of a series of transversely oriented individual rollers mounted or supported in end-to-end relation on a common transverse support or saddle frame, and mounted so that the running surfaces of the rollers define the desired troughing angle.
Impact rollers are, themselves, subject to premature and often unpredictable failures. For example, the idler bearings may fail due to the high loading or due to spill-overs or contamination from the material being carried, or from dust. Also, the impact roller surface may become damaged or out of round. When a bearing or impact idler fails, the impact roller can jam, causing damage to the belt or requiring shut down of the conveyor system.
A number of solutions have been proposed, most of which require the reconstruction of the impact zone by the substitution of a slider bed in the zone. A typical slider bed, also known as a belt cradle assembly, is shown in Andersson, U.S. Pat. No. 4,793,470 issued Dec. 27, 1988. The series of impact rollers is replaced by a single cradle at the impact area, the cradle is formed with a series of longitudinally extending, transversely spaced slats or bars formed of high molecular weight polymer material, cushioned by a rubber underlayer. Such slider beds are particularly effective in providing a long wearing belt support, at the impact zone, and in eliminating the problems of failures of impact idlers.
The principal disadvantage of the impact zone slider beds, of the general kind shown in Andersson, resides in the relatively high initial cost of the conversion to such a slider bed, usually requiring a shut down and redesign of the conveyor system, to accept a slider bed at the impact zone. Also, in the event it should become necessary to repair or replace one of the longitudinal bars, this usually requires a shut down of the conveyor since the bars are usually only accessible from a position beneath the upper run of the belt.
A need exists for an improved impact idler, which can be substituted directly for an existing idler, and provide the advantages which are afforded by costly conversion to a bar-type impact bed or slide assembly.